1. Field of the Invention
The present invention relates to power supplies. More particularly, the present invention relates to a method and apparatus of providing power to circuitry utilizing two different power sources.
2. Description of the Related Art
Over the past few decades, commercial aircraft has become a necessary mode of travel for personal and business reasons. To improve passenger comfort, commercial aircraft typically offer a number of entertainment activities that can be enjoyed by the passenger, such as video games, movies and various selections of music. In addition, various electronic systems for supporting communications and/or other in-flight functions are provided.
Such electronic systems typically comprise electronic units which receive in-flight entertainment programs from a central system and which subsequently deliver these programs to one or more passengers on the aircraft. These electronic units typically include circuitry which draw power from two different power sources, such as a +5 V power supply and a +3.3 V power supply which in turn obtain power from a 12 V regulator. The +5 V and +3.3 V power supplies typically provide the current and voltage requirements of microcontrollers and processors respectively. When operational, the microcontroller issues a control signal to the processor to reset, to boot or to initialize the processor. However, in such conventional systems, the control signal issued by the microcontroller is sometimes issued to the processor before the processor has been powered up or before the integrity of the processor has been validated. The control signal is then treated as an invalid request and the processor remains in an unreset, unbooted or uninitialized state even upon powering up.
Moreover in such conventional systems, when the output of the 12 V regulator is terminated, the +5 V power supply is typically terminated before the +3.3 V power supply is terminated. This may result in damaging circuits which are still operating on the +3.3 V power supply, if back biasing of various components in those circuits, as provided by the +5 V power supply, is terminated.
Accordingly, there is a need in the technology for an apparatus and method for providing power utilizing two different power sources, so that circuitry relying on both power sources may issue appropriately-timed control signals, to maintain circuit integrity when either one of the power supplies is turned off.